Start with the piece.
Ask for the actual size information and garment measurements for the item you are considering. A generic label or your usual size cannot confirm how a particular piece will fit.
Say what you prefer.
Relaxed or closer to the body, a certain length, a sleeve preference or room for a layer: these details can make a question more useful than a size label alone.
Keep assumptions out of it.
Confirm materials, lining, stretch information and the relevant measurements rather than inferring them from a photograph. The style references on this site are not size or material specifications.
Ask a fit question